A. Field of the Invention
The present invention relates generally to manipulator welding apparatus equiped with a vision system for weld seam tracking and more particularly to an improved image sensing and welding arrangement for such manipulator apparatus.
B. Description Of The Prior Art
Various vision detection systems have been proposed for use in connection with manipulator welding apparatus. For example, Masaki U.S. Pat. No. 4,380,696 and Masaki et al application Ser. No. 307,174 now U.S. Pat. No. 4,492,847 both disclose arrangements wherein separate manipulator hands are provided for the welding torch and an image sensing unit. In Masaki U.S. Pat. No. 4,380,696 the image sensing hand includes an optical pattern projector and a solid state TV camera, the optical pattern projector providing a light slit pattern on the workpiece which is viewed by the TV camera to provide an image representing the welding area during both a teaching phase in which a reference image is stored and during playback cycles during which the image corresponding to each workpiece is stored and employed to correct the stored program of the manipulator. In Masaki et al application Ser. No. 307,174 the image sensing hand comprises an optical pattern projector and a lens system which is connected by means of a fibre optic cable to a remotely located camera unit. In both of these two hand arrangements, considerable time is lost in picking up and setting down each hand during a particular welding operation. Also the space required to store both the welding torch hand and the image sensing hand when not being used is undesirable in many instances.
Both Masaki U.S. Pat. No. 4,308,696 and Masaki et al application Ser. No. 307,174 appreciate that it is desirable to remove the image sensing unit from the welding environment during the actual welding of the seam so that the vision system is not exposed to the welding environment and optical noise resultingtherefrom. When separate image sensing hands are provided the image sensing unit is automatically removed from the welding environment but suffers from the disadvantages mentioned above. In an effort to eliminate the requirement of picking up and setting down individual welding gun and image sensing hands, both the Masaki patent and the Masaki et al application disclose alternative arrangements wherein the manipulator hand is provided with both the welding torch and image sensing units. In Masaki U.S. Pat. No. 4,308,696 the manipulator hand carries an arrangement in which the weld torch tip is located diametrically opposite the optical center point of the image sensing unit and the manipulator hand is then rotated 180.degree. to move the image sensing unit above the workpiece when the weld torch is performing an actual welding operation. In Masaki et al application Ser. No. 307,174, the image sensing unit is rotated to a point above the welding torch after the first image sensing pass over the workpiece so that it is vertically above the workpiece during the actual welding operation. In both of these prior art arrangements, the image sensing unit is still relatively close to the welding environment and the optical lens system suffers deleterious effects from the fumes and splatter during the actual welding operation. Also, these arrangements for rotating the image sensing unit to a point above the welding torch require substantial additional space which may interfere with the welding operation due to clearance problems with obstructions on or around the workpiece being welded.